Fix unit tests and minor touchups

Author: chusitoo

exporters/otlp/test/otlp_http_exporter_test.cc

@@ -747,7 +747,7 @@ TEST_P(OtlpHttpExporterRetryIntegrationTests, StatusCodes)
         return response.code;
       }};
   HTTP_SERVER_NS::HttpServer server;
-  server.setKeepalive(false);
+  server.setKeepalive(true);
   server.setServerName("test_server");
   server.addHandler("/v1/traces", request_handler);
   ASSERT_EQ(server.addListeningPort(4318), 4318);

ext/src/http/client/curl/http_client_curl.cc

@@ -801,7 +801,7 @@ bool HttpClient::doRetrySessions()
        retry_it != pending_to_retry_sessions_.crend();)
   {
     const auto session   = *retry_it;
-    const auto operation = (nullptr != session) ? session->GetOperation().get() : nullptr;
+    const auto operation = session ? session->GetOperation().get() : nullptr;
 
     if (!operation)
     {

ext/src/http/client/curl/http_operation_curl.cc

@@ -444,7 +444,8 @@ bool HttpOperation::IsRetryable()
   const auto is_retryable = std::find(kRetryableStatusCodes.cbegin(), kRetryableStatusCodes.cend(),
                                       response_code_) != kRetryableStatusCodes.cend();
 
-  return is_retryable && retry_attempts_ < retry_policy_.max_attempts;
+  return is_retryable && (last_curl_result_ == CURLE_OK) &&
+         (retry_attempts_ < retry_policy_.max_attempts);
 }
 
 std::chrono::system_clock::time_point HttpOperation::NextRetryTime()
@@ -1404,6 +1405,8 @@ void HttpOperation::PerformCurlMessage(CURLcode code)
     ReleaseResponse();
     // Rewind request data so that read callback can re-transfer the payload
     request_nwrite_ = 0;
+    // Reset session state
+    DispatchEvent(opentelemetry::ext::http::client::SessionState::Connecting);
   }
   else
   {